Added __getstate__ and __setstate__ to DotedDict and i18nDotedDict.

Noticed that I was receiving a Python error:
   ...
   dict = getstate()
   TypeError: 'NoneType' object is not callable
   ...

when trying to cPickle.dumps a MongoKit document.  I noticed that occurred because a field in my doc was treated as a mongokit.helpers.DotedDict rather than a normal dict.  It appears that without explicitly stating \_\_getstate__ and \_\_setstate__ as a normal dict, the pickling fails.  I have added these functions.  Never know when you need to pickle these objects.